The Use of Photoelastic Technology in the Localization of Strain on the Equine Hoof Wall: An In Vitro Pilot Study
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As horses place weight upon their hooves, the hoof wall deforms to absorb the stress of impact. This results in strain upon the hoof wall. High levels of strain can predispose the hoof to pathological conditions. In the past, strain gauges have been used to determine strain in the equine foot. However, due to the questionable placement of these gauges and the restriction in their localized measurements, the results are unreliable. A more qualitative technique for assessing the location and magnitude of strain on the equine hoof is necessary. The goal of this study is to employ the technique of Photoelastic Stress Analysis (PSA) to examine the distribution of strain on normal equine hooves. Cadaveric hooves were coated with photo elastic plastic. Then the hooves were mechanically loaded and viewed using polarized light. As deformation of the hoof wall occurred under load, strain of the hoof wall was manifested by optical bands of color. The hooves were loaded under normal anatomic positioning as well as varus, valgus and frontal angulation. The resulting strain patterns showed a consistency in location, although the intensity of the areas were found to vary with varus and valgus positioning. The strain patterns were localized in the distal and middle thirds of the lateral and medial sides of the hoof wall. These strain patterns coincided with the location of the anatomical bond between the hoof and the bone. Previous studies have indicated that expansion of the hoof wall is restrained in this area. The results of this study support the use of PSA to evaluate strain patterns on the equine hoof. The next phase of this study will examine the possibility of using this technique to determine how various hoof ailments may alter the magnitude and/or location of strain within the hoof wall. Subsequent studies could then use this technique to evaluate the effects of various methods of corrective shoeing and trimming.